US Publication 2013/0316428 describes a process in which an organic fraction containing biological cells is separated from solid urban waste. The organic fraction is extruded through a grid having small-bore holes, under a pressure higher than the burst pressure of the cell membranes. The cells are disrupted and a gel of a doughy consistency is produced. The gel is then loaded into a biodigester, where it is readily attacked by bacteria. The press may be as described in European Publication Nos. 1207040 and 1568478. In general, these presses use a plunger to compress waste that has been loaded into a cylinder. The sides of the cylinder are perforated with radial holes. US Publication 2013/0316428 and European Publication Nos. 1207040 and 1568478 are incorporated herein by reference.